Locomotive propulsion systems commonly use high horsepower electric traction motors connected through suitable gearing to drive wheel/axle sets. Each wheel axle set includes an axle, a pair of wheels and a drive gear mounted to the axle. Both the wheels and drive gear are press fit on the axle. The drive gear is located adjacent to and inboard of one of the wheels on one end of the axle. The area of the axle at which the drive gear and adjacent wheel is mounted is a highly stressed area and for that reason there is generally a circumferential stress relief groove formed around the axle between the drive gear and wheel. Both the gear and wheel include an enlarged hub portion in press fit relation to the axle. During operation of the locomotive, the torque transmitted to the wheels through the drive gear pressed on the axle may cause the gear hub to slip slightly from its normal spaced position with respect to the hub of the wheel. One of the functions of the gear hub is to provide an axial position limit for a gear side cone of a tapered roller bearing which supports part of the weight of the traction motor on the axle. Small axial movement of the gear in a direction which would reduce the space between the gear hub and wheel hub results in an increase in the clearance in the traction motor to axle support bearings and a reduction in their anticipated fatigue life. Accumulated small axial movements of the gear hub may result in bearing clearances sufficiently large that undesirable contact between rotating and static structural members of the axle support assembly may occur. Accordingly, it is desirable to provide some means for maintaining the spacing of the gear hub from the wheel hub.
During the process of assembling the wheel/axle set, one wheel may be pressed onto one end of the axle followed by pressing the drive gear onto an opposite end of the axle. Finally, the second wheel is pressed onto the opposite end of the axle adjacent the drive gear. Historically, the position of the second wheel is determined by a measuring rod placed between the one and the second wheel. Because this measurement extends over feet, there is often some small error in measurement which varies the spacing between the axle hub and wheel hub. Since this spacing (wheel to wheel) is critical, any error requires an expensive dismounting of the gear side wheel and remounting. Accordingly, it is desirable to provide some means for better establishing the spacing of the gear hub and wheel hub.